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From: Avi Kivity <avi@redhat.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Huang Ying <ying.huang@intel.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	linux-kernel@vger.kernel.org, Andi Kleen <andi@firstfloor.org>,
	Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Subject: Re: [PATCH 8/5] llist: Remove cpu_relax() usage in cmpxchg loops
Date: Tue, 13 Sep 2011 14:43:39 +0300	[thread overview]
Message-ID: <4E6F41EB.1040106@redhat.com> (raw)
In-Reply-To: <1315837930.26517.49.camel@twins>

On 09/12/2011 05:32 PM, Peter Zijlstra wrote:
> On Mon, 2011-09-12 at 17:26 +0300, Avi Kivity wrote:
> >  On 09/12/2011 05:05 PM, Peter Zijlstra wrote:
> >  >  Subject: llist: Remove cpu_relax() usage in cmpxchg loops
> >  >  From: Peter Zijlstra<a.p.zijlstra@chello.nl>
> >  >  Date: Mon Sep 12 15:50:49 CEST 2011
> >  >
> >  >  Initial benchmarks show they're a net loss (2 socket wsm):
> >  >
> >  >    $ for i in /sys/devices/system/cpu/cpu*/cpufreq/scaling_governor ; do echo performance>   $i; done
> >  >    $ echo 4096 32000 64 128>   /proc/sys/kernel/sem
> >  >    $ ./sembench -t 2048 -w 1900 -o 0
> >  >
> >
> >  We hyperthreading enabled, and were all threads loaded?  cpu_relax
> >  allows the other thread to make more progress while the spinner relaxes.
>
> Yeah, with HT enabled, the benchmark runs 2048 tasks and does 1900 task
> bulk wakeups or so. Forgot the details, but it basically stresses the
> sleep+wakeup paths like nobodies business.

Ok.

Another issue is that hypervisors use PAUSE to detect a spinning guest 
and issue a directed yield to another vcpu.  But for cmpxchg loops, the 
"spinner" would just commit on the next loop, no?  So I think there's no 
objection from that front.

-- 
error compiling committee.c: too many arguments to function


  reply	other threads:[~2011-09-13 11:43 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-09-08  6:00 [PATCH -mm -v2 0/5] irq_work, Use llist in irq_work Huang Ying
2011-09-08  6:00 ` [PATCH -mm -v2 1/5] llist, Make all llist functions inline Huang Ying
2011-09-08  6:00 ` [PATCH -mm -v2 2/5] llist, Define macro to check NMI safe cmpxchg Huang Ying
2011-09-08  6:00 ` [PATCH -mm -v2 3/5] llist, Move cpu_relax after cmpxchg Huang Ying
2011-09-08  6:00 ` [PATCH -mm -v2 4/5] llist, Return whether list is empty before adding in llist_add Huang Ying
2011-09-08  6:00 ` [PATCH -mm -v2 5/5] irq_work, Use llist in irq_work Huang Ying
2011-09-12 14:05 ` [PATCH 6/5] llist: Add llist_next() Peter Zijlstra
2011-09-12 14:05 ` [PATCH 7/5] sched: Convert to use llist Peter Zijlstra
2011-09-12 14:05 ` [PATCH 8/5] llist: Remove cpu_relax() usage in cmpxchg loops Peter Zijlstra
2011-09-12 14:23   ` Andi Kleen
2011-09-12 14:23     ` Peter Zijlstra
2011-09-12 14:47     ` Mathieu Desnoyers
2011-09-12 15:09       ` Peter Zijlstra
2011-09-12 15:24       ` Peter Zijlstra
2011-09-12 16:38       ` Andi Kleen
2011-09-12 18:53         ` Peter Zijlstra
2011-09-12 14:26   ` Avi Kivity
2011-09-12 14:32     ` Peter Zijlstra
2011-09-13 11:43       ` Avi Kivity [this message]
2011-09-13 14:22         ` Peter Zijlstra
2011-09-13 14:51           ` Avi Kivity
2011-09-13 14:53             ` Peter Zijlstra
2011-09-12 14:06 ` [PATCH -mm -v2 0/5] irq_work, Use llist in irq_work Peter Zijlstra

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